A method for the manufacture of molded products by the reaction injection molding (RIM) method using norbornene monomers, such as dicyclopentadiene (DCPD) and methyl tetracyclododecene, as molding materials has drawn attention in recent years to a wide range of fields such as automotive, electrical, electronic, civil engineering, house furnishings and leisure products. These molded products are often coated or painted in order to improve their appearance. Furthermore, it has been required to obtain many moldings in an as short a period of time as possible, from the viewpoint of productivity during manufacturing.
However, if a norbornene monomer or a mixture thereof is allowed to react inside a forming mold, a problem frequently occurs in which the molded product cannot be easily released or extracted from the mold. Therefore, a variety of mold-releasing agents have been used. However, for the RIM method using norbornene monomers, suitable mold-releasing agents have not been discovered to date.
Known mold-release agents for molds include silicone, mineral oils, wax, fatty acid derivatives, glycol, and other natural or synthetic compounds as such or diluted with solvents, talc, silica, alumina, mica, or other inorganic substances dispersed in solvents, or used in combination with wax in a paste form. In general, these mold-release agents are coated prior to the introduction of the molding materials into the molds.
In the urethane RIM method, natural or synthetic waxes are commonly used as mold-release agents because of their low cost. Examples of such mold-release agents include esters of fatty acids and monovalent or polyvalent alcohols, wood wax and other plant waxes, beeswax, lanolin and other animal waxes, paraffin, microcrystalline and other petroleum waxes, montan wax and other coal waxes, polyolefins, hydrocarbon oligomers and other synthetic waxes.
However, if these mold-release agents are used in the RIM method utilizing norbornene monomers as the molding materials, the polymerization reactivity of the monomers is hindered and it is difficult to obtain excellent molded products having smooth and lustrous surfaces. Moreover, since the norbornene monomers have an effect as an organic solvent, they may dissolve the mold-release agents in some cases. As a result, there is a problem of reducing mold-release effectiveness.
Silicone is the most commonly used mold-release agent because of its good mold-release characteristics. However, if the norbornene monomers are used as molding materials, the surface will become white when the molded products with good mold-release characteristics are released from the molds. This is known as the whitening phenomenon. Therefore, there is a problem of decreasing the commodity value of the molded products. Furthermore, silicone oils move readily or permeate into the molded products. Coating or adhesion processing of surfaces of such molded products is difficult. Since the molded products obtained by the RIM method often require coating, an improvement in their coatability is a technologically important topic.
If an inorganic substance, such as talc or silica, is used in combination with wax, glycol, or the like as a mold-release agent, it will be necessary to use a relatively large amount of the mold release agent. If molding is continued under these conditions, the residue of the mold-release agent or the molded product will remain in the corners of the mold. As a result, the mold must be cleaned often and the molding operation efficiency will decrease.
It is known that compounds containing fluorine have a low surface energy. In the urethane RIM method, the fluorine-containing compound is utilized in combination with the previously described wax or silicone oil, talc, silica, or the like as the mold-release agent. These combination mold-release agents have the problem described previously when the norbornene monomers are used as the molding materials. Furthermore, if the fluorine compounds are used alone, it is said that their mold-release effectiveness will decrease.
In the case of molds for creating a delustered or cloudy condition in the molded product, without surface tackiness, there are many microfine concave-convex portions on the surface of the molds. As a result, the conventional mold-release agents collect readily in the concave portions and uniform coating is difficult. In addition, in the case of the mold-release agents without lasting mold-release effectiveness, it will be necessary to coat the mold-release agents repeatedly for each of the various molding cycles. Such operation has been one of the causes of the reduction of productivity.
In the method for the manufacture of the molded products by the RIM method using the norbornene monomers as the molding materials in this manner, it is required to have mold-release agents which have good operability, increased molding cycles, no occurrence of poor molding or whitening of the surfaces of the molded products, and no adverse effects on secondary processing, such as coating and adhesion.